Electron discharge apparatus



July 14, 1953 J. H. FREMLIN ETAL ELECTRON DISCHARGE APPARATUS Filed June 2, 1942 Arron/5y Patented July 14, 1953 burrs stares rear f Fries ELECTRON DISCHARGE APPARATUS Delaware Application June 2, 1942, Serial No. 445,502

In Great Britain May 2 1, 1940 Section 1, Public Law 690, August s, 1946 Patent expires May 24, 1960 6 Claims.

This invention relates to electron discharge apparatus for operation at ultra-high frequencies and of the kind in which pulses of electrons or bunched electrons set up for example by velocity modulation of an electron beam are utilised to excite a high frequency resonator.

In accordance with the invention the pulses of electrons or the bunched electrons are utilised as primary electrons to produce at a secondary emissive surface a discontinuous or non-uniform stream of secondary electronsfor the excitation of the high frequency resonator.

The apparatus may comprise means for directing a beam of electrons through a high frequency field having a component parallel to the beam and for bunching the resulting velocity modulated electrons, a secondary emissive electrode arranged to be bombarded by the bunched electrons and means for withdrawing the resulting secondary electrons and for passing them through a high frequency field to yield up energy by retardation. The high frequency fields may be set up in the known way by separate resonators or double resonators of the cavity type or they may be set up by a single cavity resonator providing suitable fields at spaced regions along the electron path.

In velocity modulated apparatus it is usual for the electron beam to be controlled at one part of the apparatus and for work to be done by it at another part, for example in some form of resonator. In order to obtain high powers attempts have been made to get very large current densities in the electron beam. This involves difficulties in maintaining the concentration of the beam through the whole system as well as in obtaining high power cathodes. It is therefore proposed that the beam be allowed to fall on a secondary emitting electrode just before crossing the working gap but after bunching. A high potential may be maintained between this electrode and the other side of the resonator, the previous parts of the tube being at fairly low potentials.

The secondary emitting electrode may take the form of a grid of metal suitably treated to be highly emissive under electron bombardment. It may alternatively be possible to employ thin films as already proposed which emit electrons from one side when bombarded on the other. The emission of secondaries being instantaneous the bunching is not adversely affected. Apart from the increased power obtainable, other advantages exist, for example there is only a relatively small voltage on most of the apparatus and none of the electrons lost by divergence of the beam waste high tension energy.

The accompanying figure-shows diagrammatically an apparatus of the klystron type in accordance with the invention. Details of construction, or of power supply or associated electrical circuits for the operation of the device are not shown; all such details may be provided in any of a number of known ways Well understood by those skilled in the art. 7 V

The device consists of a pair of toroidal metal resonators RI and R2 arranged with their axes in line and separated by an axial drift tube T. By suitable means, an axial beam of-' electrons generated by a cathode C is projected from the left hand side, through two central grids G5 and G2 forming part of the resonator Rt and centrally placed as, shown. The beam becomes velocity modulated in its passage through the resonator RI and then travels through the drift tube T in which the electrons become bunched. The electrons strike the central grid'A which forms part of the resonator R2. The grid A is treated so as to become an efficient secondary emitter and the secondary electrons produced thereby travel forwards with the original beam. The electrons then strike the electrode B atthe rear of the central portion of R2, but insulated therefrom, where they are finally collected. The electrode B will be maintained at a direct potential higher. than that of R2, but should be coupled thereto through a suitable condenser such as K.

In operation of the apparatus, the primary electron beam is modulated in velocity in passing through the resonator RI, and is bunched in the drift tube T so that it strikes the secondary emissive grid A in a series of high frequency pulses. Pulses of secondary electrons of similar frequency but of greater intensity are then emitted for the excitation of the resonator R2. The resonator RI may be excited from an external source so that the apparatus functions as an amplifier, or the two resonators may be regeneratively coupled for operation as an oscillator in known fashion. As an indication of the order of voltages to be used for operating the device, a primary beam set up by a voltage of the order of 400 or 600 volts may be employed; the resonators will normally have the same potential; the collecting electrode may have a voltage applied to it of the order of 5000 or 10,000 volts.

While the invention has been described in connection with a particular type of embodiment, it is not limited thereto, and other embodiments to which the features of the invention are applicable will occur to those skilled in the art.

What is claimed is:

1. An electron discharge device comprising means for generating a beam of electrons, means for directing said beam along a predetermined path, means for velocity modulating said beam and causing the bunching of the electrons comprising a cavity resonator and a drift tube, a secondary emissive electrode and a cavity resonator in succession placed; in the path of said beam, said secondary emissive electrode placed effectively between said drift tube and said cavity resonator last named and responsive to said bunched electrons for electrically exciting said cavity resonator last named.

2. An electron discharge device, accordingtoclaim 1, wherein said cavity resonator has an entrant opening, wherein said secondary emissive electrode comprises a thin film of electron emissive material having sides transverse to the bunched electron beam, said material when bombarded withbunched electrons on one side emits secondary electrons from the other side, said electrode being integral with said cavity resonator at saidentrant opening.

3. An electron discharge device comprising means for producing a beamv of electrons, means for directing said beam. along a predetermined path, means for velocity modulating the electrons of said beam and causing the bunching of the electrons, a secondary emissive electrode and a cavity resonator in succession placed in the path of said beam of electrons, said secondary emissive electrode placed effectively between said velocity modulating-bunching means and Said last named. cavity resonator, means for electrically excitingv said cavityresonator comprising said. secondary emissive electrode responsive in part to said bunched electrons.

4. An electron discharge device, according to claim 3, wherein said cavity resonator has an entrant opening, said secondary emissive electrode comprising ametal grid treated to be highly means for producing an electron beam, means positioned adjacent the path of the beam for varying the velocities of the electrons thereof, a drift space enclosure comprising a body of electrical conducting material having an opening extending therethrough and in alignment with the course of the electrons to permit the beam to pass through the opening within the drift space enclosure and to become density varied, a'secondary electron emitting surface positioned in. the path of the beam and upon which the density-varied beam impinges tocause emission of a beam of secondary electrons and output means. within the device electrically coupled to the beam of secondar electrons to extract output energy therefrom.

- JOHN HEAVER FREMLIN. v

ROGER NORMAN HALL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,287,845 Varian et al June 30, 1942 2,295,396 George Sept. 8-, 1942 2,295,680 Mouromtseff et al. Sept. 15, 19.42 2,408,423 Hartley Oct. 1, 1946 2,416,302 Goodall Feb. 25, 1947 

